A sputtering method is widely employed at present to form a thin film of a wiring material for use in an integrated circuit. This is a process of forming a thin film by introducing Ar gas into a vacuum vessel and applying DC or high frequency power to a cathode having a target material mounted thereon to produce glow discharge. As a result of the glow discharge, a target surface is biased to a negative potential with respect to a plasma (called a self-bias), and Ar ions accelerated by the bias voltage impinge on the target surface to sputter and etch the target material. Material particles sputtered from the target are deposited on a wafer placed in opposition to the cathode to form a thin film. Another method, a high frequency bias-sputtering method is known, wherein high frequency power is applied not only to a target but to a susceptor itself on which a wafer is mounted to deposit a film on a wafer surface while permitting sputtering and etching to be effected simultaneously with the aid of the self-bias formed on the wafer surface. Referring here to FIG. 5, illustrating the arrangement of a typical prior bias-sputtering device in a cross section, designated at 501 is for example a target made of Al or SiO.sub.2, and 502 is a target electrode having a target mounted thereon. In addition, designated at 503 and 504 are respectively a semiconductor wafer and a susceptor electrode. The target electrode 502 and the susceptor electrode 504 are respectively supplied with high frequency power via a matching circuit, and the vacuum vessel 505 is grounded. For the high frequency power source (RF power source), one having oscillation frequency of 13.56 mHz is typically employed. Moreover, means other than those described above: a vacuum exhaust system, gas introduction inlets, and a mechanism for inserting and removing the wafer are also provided, but they are not shown in the figure for clarity.
The surfaces of the semiconductor wafer 503 and the susceptor 504 are self-biased negatively with respect to the plasma by the RF power applied to the susceptor, on which surfaces Ar ions accelerated by the electric field of the self-biased potential then impinge to sputter part of the deposited film. This method assures a thin film excellent in mechanical strength. This method is furthermore characterized by forming a flat surface film by making use of the fact that the film formed near a stepped portion is likely to be sputtered. This method, however, suffers in practical use from the problem that the etching effected simultaneously with the film deposition causes the speed of film formation to be severely reduced. Furthermore, another significant problem in the manufacture of semiconductor integrated circuits is produced wherein the impingement of Ar ions accelerated by the self-bias on the semiconductor wafer damages the substrate, thereby resulting in deterioration of the constituent elements. These problems are severe obstacles to the practical use of the bias-sputtering apparatus.
The present invention, in view of the drawbacks of the prior semiconductor manufacturing methods, has provided a semiconductor manufacturing apparatus capable of forming a high quality thin film at a sufficiently high speed of film formation without damaging the substrate.